Method for preparation of aluminum matrix composite

ABSTRACT

Disclosed is a method for preparation of an aluminum matrix composite including preparation of in-situ reaction mixed salt, preparation of a TiB2 enhanced 6061 aluminum matrix composite and ultrasonic treatment of a composite melt. The obtained composite contains TiB2 enhancing particles which are fine in size and uniform in distribution and may remarkably improve the mechanical performance indicators of a matrix alloy. In the TiB2 enhanced 6061 aluminum matrix composite according to the present disclosure, the size of the TiB2 enhancing particles is 200-500 nm and the particles are uniform in distribution in the matrix alloy.

FIELD

The present disclosure relates to the technical field of aluminum alloys, in particular to a method for preparation of an aluminum matrix composite.

BACKGROUND

The 6061 aluminum alloy is one of the most widely applied Al—Mg—Si wrought aluminum alloys. Due to its relatively good mechanical properties, excellent corrosion resistance and good weldability and molding performance, the 6061 aluminum alloy is broadly applied to the automobile industry. With the rapid development of the automobile industry, more and more vehicle parts are made of the 6061 aluminum alloy. In the meantime, issues such as energy supply shortage and severe exhaust pollution caused by the automobile industry are becoming worse. In particular, under the strict limitations of automobile energy efficiency standards in all countries, energy conservation, environmental protection, higher driving safety and higher driving comfort become critical challenges that automobile manufacturers have to face. Given the above Situation, lightweight technology is being applied to all parts of an automobile. Although aluminum alloys are broadly applied to replace steel and iron materials for automobiles and realize a remarkable weight reducing effect, the bearing capacity of parts is greatly reduced while weight is largely reduced, as a result, the large-scale application of the aluminum alloys to loaded parts is limited. The particle enhanced aluminum matrix composite has considerable application potentials in the field of automobile parts due to its low density, high specific stiffness, high specific strength, low expansion, high heat conduction and other features.

In the study on a technology for the preparation of the particle enhanced aluminum alloy composite, methods of adding reinforcements, such as powder metallurgy and stir casting, have long been used. These methods cost high, reinforcements and aluminum matrices are poor in interfacial wettability, and plasticity and toughness of materials decreases greatly, accordingly, the application of the methods to production of automobile parts is limited. An in-situ synthesis technology for the preparation of the aluminum matrix composite may effectively solve the above problems. The in-situ synthesized aluminum matrix composite has the advantages such as fine enhancing particles, clean particle and matrix interface and high compatibility that are incomparable by methods of addition. In an existing in-situ synthesis technology, the method for the preparation of the TiB₂ particle enhanced aluminum matrix composite by reactions between KBF₄ and K₂TiF₆ mixed salt and an aluminum melt is simple in process and low in cost, thereby having good industrial prospects. However, in the prior art, on one hand, TiB₂ enhancing particles have a large size (about 1 μm), and on the other hand, TiB₂ particles may suffer a severe aggregation phenomenon. Those are the problems having to be settled urgently in the process of the preparation of the in-situ synthesis aluminum matrix composite.

SUMMARY

For this purpose, the present disclosure aims to provide a method for preparation of an aluminum matrix composite. The aluminum matrix composite prepared by the method contains TiB₂ particles fine in size and uniform in distribution.

To make the objectives, the technical solution of the present disclosure is implemented as follows:

The method for preparation of the aluminum matrix composite includes the following steps:

S1, evenly mixing a reaction salt KBF₄ powder, a reaction salt K₂TiF₆ powder and a reaction auxiliary Na₃AlF₆ powder in a V-type mixer;

S2, drying the powder mixed in the step S1;

S3, putting commercial purity aluminum in a resistant furnace, heating and melting the commercial purity aluminum and overheating to 800-810° C.;

S4, upon stripping off oxide scale on the surface of the melt, evenly scattering the mixed powder in the step S2 onto the surface of the melt by a powder sprayer, melting the mixed powder to form a flux layer that floats on the surface of the melt, controlling reaction temperature, and maintaining the temperature for a certain period;

S5, upon stripping off reaction salt residues on the surface, performing mechanical agitation on the melt;

S6, sequentially adding alloys of Si, Cu, Cr, Mn, Ti, Zn and Mg, and maintaining the temperature for a certain period to completely melt the elements of the alloys;

S7, evenly scattering a slag-cleaning agent onto the surface of the melt by a powder sprayer, introducing high-purity argon with a flow rate of 3 L/h, performing mechanical agitation, stirring and degassing for 5 min, and then stripping off scum on the surface;

S8, performing ultrasonic treatment on the melt in the step S7 at an ultrasonic frequency of 20.1 KHz for 10 min; and

S9, pouring the melt into a metal mold.

In some embodiments, in the step S2, the mixed powder is dried at 200-250° C. for 2-3 h.

In some embodiments, in the step S1, an atomic ratio of Ti to B in the K₂TiF₆ powder and the KBF₄ powder is preferably 1:2, and an addition amount of the reaction auxiliary Na₃AlF₆ powder is 10-20% of the total mass of the reaction salt K₂TiF₆ and the reaction salt KBF₄.

In some embodiments, in the step S4, the reaction temperature is maintained in the range of 830-850° C. for 30-60 min.

In some embodiments, in the step S5, the speed of the mechanical agitation is 250-350 r/min, and the time for the mechanical agitation is 3-5 min.

In some embodiments, in the step S6, the elements Si, Cr and Mn are respectively added in the form of intermediate alloys AlSi20, AlCr10, AlMn10 and AlTi20, the elements Cu, Zn and Mg are added in the form of pure metals, and the temperature is maintained in the range of 730-750° C.

In some embodiments, in the step S7, the speed of the mechanical agitation speed is 250-350 r/min.

In some embodiments, in the step S9, the pouring temperature is in the range of 705-710° C.

Compared with the prior art, the method for the preparation of the aluminum matrix composite of the present disclosure has the following advantages:

The method of the present disclosure is simple in process, low in cost and beneficial for mass production, and the composite prepared by the method of the present disclosure contains TiB₂ enhancing particles fine in size and uniform in distribution and may remarkably improve mechanical performance indicators of a matrix alloy.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings as one part of the present disclosure provide a further understanding of the present disclosure, and exemplary embodiments of the present disclosure and description thereof are provided to interpret the present disclosure, but not to improperly limit the present disclosure. In the accompanying drawings:

FIG. 1 is a structure scan electron microscope image (Mag=200 X) of an aluminum matrix composite prepared by a traditional preparation method.

FIG. 2 is a structure scan electron microscope image (Mag=200 X) of an aluminum matrix composite prepared by a preparation method of the present disclosure.

FIG. 3 is a structure scan electron microscope image (Mag=15.00 KX) of the aluminum matrix composite prepared by the traditional preparation method.

FIG. 4 is a structure scan electron microscope image (Mag=15.00 KX) of the aluminum matrix composite prepared by the preparation method the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

It should be noted that the embodiments of the present disclosure and features in the embodiments may be combined with each other under no conflicts.

The technical solutions of the present disclosure will be clearly and comprehensively described as below by reference to the accompanying drawings in conjunction with the embodiments. Obviously, the embodiments as described herein are only part of the embodiments of the present disclosure, but not to represent all the embodiments. All other embodiments that those of ordinary skill in the art may acquire without making creative efforts all belong to the protection scope of the present disclosure.

The method for preparation of the aluminum matrix composite of the embodiments of the present disclosure is described in conjunction with the embodiments by reference to FIGS. 1-4 as below.

The method for preparation of the aluminum matrix composite includes the following steps:

S1, mixing KBF₄ powder, K₂TiF₆ powder and Na₃AlF₆ powder in a V-type mixer for 50 min;

S2, drying the mixed salt in a blast drying oven at a drying temperature in the range of 200-250° C. for 2-3 h;

S3, heating and melting commercial purity aluminum in a resistant furnace, and overheating until a temperature of the melt is in the range of 800-810° C.;

S4, after stripping off oxide scale on the surface of the melt, evenly scattering the mixed salt obtained in the step Si onto the surface of the melt in the step S3 by a powder sprayer, melting the mixed salt to form a flux layer that floats on the surface of the melt, controlling a reaction temperature to be in the range of 830-850° C., and maintaining the temperature for 30-60 min while not performing agitation;

S5, after stripping off salt residues on the surface of the melt in the step S4, performing agitation by a graphite rotor at a revolution speed in the range of 250-350 r/min for 3-5 min;

S6, sequentially adding alloys of AlSi20, AlCr10, AlMn10, AlTi20, pure Cu, pure Zn and pure Mg to the melt in the step S5 according to the standard composition of the 6061 aluminum alloy while maintaining the melt temperature not higher than 760° C., and maintaining the temperature at 750° C. to completely melt the alloys;

S7, evenly scattering a slag-cleaning agent onto the surface of the melt in the step S6 by a powder sprayer, introducing high-purity argon with a flow rate of 3 L/h, performing mechanical agitation, stirring and degassing for 5 min, and then stripping off scum on the surface;

S8, performing ultrasonic treatment on the melt in the step S7 at an ultrasonic frequency of 20.1 KHz for 10 min; and

S9, pouring the melt obtained in the step S8 into a metal mold at a pouring temperature in the range of 705-710° C.

Compared with an aluminum powder and reaction salt ball-milling, mixing and sintering process adopted in other preparation methods, the method of the present disclosure adopts an industrial common mixer to evenly mix reaction salts, thereby being higher in efficiency and safety, simple in process and beneficial for mass industrial production.

The step S1 of adding the reaction auxiliary Na₃AlF₆ to the mixed salt accelerates the reaction rate of the mixed salt and the aluminum melt and shortens the reaction time.

By the step S4 of scattering the mixed salt onto the surface of the melt by the powder sprayer, on one hand, the contact between the mixed salt and the surface of the melt is more uniform, and compared with the means of sintering the mixed salt into cakes and adding the cakes in to the melt, the method of the present disclosure is simpler and more economical and meanwhile reduces the tendency of particle aggregation; and on the other hand, the mixed salt may react with the melt uniformly and rapidly, and thereby avoiding the severe change within a short time of the temperature of the melt during addition of a large amount of the reaction salts.

The step S5 of performing agitation on the melt may effectively disperse TiB₂ particles generated during in-situ synthesis, thereby avoiding particle aggregation and sedimentation.

By the step S8 of performing ultrasonic treatment on the melt, on one hand, blocky aggregation of TiB₂ particles is effectively cracked by an ultrasonic cavitation effect; and on the other hand, TiB₂ particles and alloy elements are more uniformly distributed by an ultrasonic acoustic streaming effect.

The method of the present disclosure omits procedures of ball-milling of the mixed salt, cold pressing into cakes and sintering in a mixed salt reaction method and thus improves material preparation efficiency and saves production cost. Meanwhile, firstly, a TiB₂ enhanced pure aluminum master alloy material is prepared, and then the TiB₂ enhanced 6061 aluminum alloy composite is prepared according to the method for the preparation of alloy elements as desired. This method avoids element burning loss in a direct high-temperature reaction process of the mixed salt and the 6061 aluminum alloy, and the aluminum matrix composite of different matrix compositions may be prepared as desired from the TiB₂ particle enhanced pure aluminum master alloy.

In some embodiments, the method for preparation of the aluminum matrix composite of the present disclosure includes the following steps:

S1, mixing 720 g of KBF₄ powder, 686 g of K₂TiF₆ powder and 210 g of Na₃AlF₆ powder in a V-type mixer for 50 min;

S2, drying the mixed salt in a blast drying oven at a drying temperature in the range of 200° C. for 2.5 h;

S3, heating and melting 10 Kg of commercial purity aluminum in a resistant furnace, and overheating until the temperature of the melt is 800° C.;

S4, after stripping off oxide scale on the surface of the melt, evenly scattering the mixed salt obtained in the step S2 onto the surface of the melt in the step S3 by a powder sprayer, melting the mixed salt to form a flux layer that floats on the surface of the melt, controlling a reaction temperature to be 850° C., and maintaining the temperature for 30 min while not performing agitation;

S5, after stripping off salt residues on the surface of the melt in the step S4, performing agitation by a graphite rotor at a revolution speed of 300 r/min for 3 min;

S6, sequentially adding alloys of AlSi20, AlCr10, AlMn10, AlTi20, pure Cu, pure Zn and pure Mg to the melt in the step S5 according to the standard composition of the 6061 aluminum alloy while maintaining a melt temperature not higher than 760° C., and maintaining the temperature at 750° C. to completely melt the alloys;

S7, evenly scattering a slag-cleaning agent onto the surface of the melt in the step S6 by a powder sprayer, introducing high-purity argon with a flow rate of 3 L/h, performing mechanical agitation at a revolution speed of 300 r/min, stirring and degassing for 5 min, and then stripping off scum on the surface;

S8, performing ultrasonic treatment on the melt in the step S7 at an ultrasonic frequency of 20.1 KHz for 10 min; and

S9, pouring the material obtained in the step S8 into a metal mold at a pouring temperature of 710° C.

The traditional method for preparation of the aluminum matrix composite includes the following steps:

(I) ball-milling 720 g of KBF₄ powder and 686 g of K₂TiF₆ powder in a ball mill (a ball-milling time of 2 h, a ball-material ratio of 5:1, a revolution speed of 150 r/min and a mode of reversely rotating every 10 min), drying the mixed salt in a blast drying oven at a drying temperature of 200° C. for 2.5 h, putting the dried powder into a mold cavity with an inner diameter of 150 mm to be cold-pressed into a round billet, and putting the round billet into the blast drying oven to be sintered at 300° C. for 30 min to obtain a compound powder sintered round billet;

(II) heating and melting 10 Kg of commercial purity aluminum in a resistant furnace, overheating until the temperature of the melt is 800° C., and stripping off oxide scale on the surface of the melt;

(III) immersing the compound powder sintered round billet in the step (I) into the melt in the step (II) until the billet is completely molten, controlling the reaction temperature to be 850° C., and maintaining the temperature for 30 min while not performing agitation;

(IV) stripping off salt residues on the surface of the melt in the step (III);

(V) sequentially adding alloys of AlSi20, AlCr10, AlMn10, AlTi20, pure Cu, pure Zn and pure Mg to the melt in the step (IV) according to the standard composition of the 6061 aluminum alloy while maintaining the melt temperature not higher than 760° C., and maintaining the temperature at 750° C. to completely melt the alloys;

(VI) evenly scattering a slag-cleaning agent onto the surface of the melt in the step (V) by a powder sprayer, introducing high-purity argon with a flow rate of 3 L/h, performing mechanical agitation at a revolution speed of 300 r/min, stirring and degassing for 5 min, and then stripping off scum on the surface; and

(VII) pouring the melt obtained in the step (VI) into a metal mold at a pouring temperature of 710° C.

FIG. 1 and FIG. 2 illustrate micro-structures (Mag=200 X) of TiB₂/6061 aluminum matrix composites prepared in Comparative Example 1 and Embodiment 1 respectively. FIG. 3 and FIG. 4 illustrate micro-structures (Mag=15 KX) of TiB₂/6061 aluminum matrix composites prepared in Comparative Example 1 and Embodiment 1 respectively. It may be illustrated by comparative analysis that in the method of the present disclosure, the mixed salt and the aluminum matrix react more thoroughly, the prepared TiB₂ particles are uniformly distributed in the matrix and have a size in the range of 200-500 nm.

Compared with the prior art, the method for preparation of the aluminum matrix composite of the present disclosure has the following advantages:

The method of the present disclosure omits procedures of ball-milling of the mixed salt, cold pressing into cakes and sintering in a mixed salt reaction method and thus improves material preparation efficiency and saves production cost. Meanwhile, firstly, a TiB₂ enhanced pure aluminum master alloy material is prepared, and then the TiB₂ enhanced 6061 aluminum alloy composite is prepared according to the method for the preparation of alloy elements as desired. This method avoids element burning loss in a direct high-temperature reaction process of the mixed salt and the 6061 aluminum alloy, and the aluminum matrix composite of different matrix compositions may be prepared as desired from the TiB₂ particle enhanced pure aluminum master alloy.

The method of the present disclosure is simple in process, low in cost and beneficial for mass production, and the composite prepared by the method of the present disclosure contains TiB₂ enhancing particles fine in size and uniform in distribution and may remarkably improve mechanical performance indicators of a matrix alloy.

In the description of the present invention, it should be understood that the terms “center”, “longitudinal”, “transverse”, “front”, “rear”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inner”, “outer”, and the like indicate orientations or positional relationships based on the drawings. The terms are only for description convenience of the present invention and simplification of the description, but do not indicate or imply that the pointed apparatuses or elements must have specific orientations or be constructed and operated in specific orientations. Therefore, the terms should not be understood to limit the present invention.

Furthermore, the terms “first” and “second” are only for the aim of description, and cannot be understood as indicating or implying the relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with “first” and “second” may explicitly or implicitly comprise one or more of these features. In the description of the present invention, “a plurality of” means at least two, e.g., two, three, etc., unless otherwise specified.

In the present invention, unless otherwise specified and defined, the terms “mounted”, “joined”, “connected”, “fixed” and the like should be understood in a broad sense, for example, being fixedly connected, detachably connected, integrated; mechanically connected, electrically connected, mutually communicated; directly connected, indirectly connected by a medium, communication of interiors of two components or interaction of two components. A person of ordinary skill in the art could understand the specific meanings of the above terms in the present invention according to specific circumstances.

The foregoing descriptions are merely preferred embodiments of the present invention, but are not intended to limit the present invention. Any modification, equivalent substitution, improvement and the like made within the spirit and principle of the present invention shall fall within the protection scope of the present invention. 

What is claimed is:
 1. A method for preparation of an aluminum matrix composite, where in the method comprises the following steps: S1, evenly mixing a reaction salt KBF₄ powder, a reaction salt K₂TiF₆ powder and a reaction auxiliary Na₃AlF₆ powder in a V-type mixer; S2, drying the powder mixed in the step S1; S3, putting commercial purity aluminum in a resistant furnace, heating and melting the commercial purity aluminum and overheating to 800-810° C.; S4, upon stripping off oxide scale on the surface of the melt, evenly scattering the mixed powder in the step S2 onto the surface of the melt by a powder sprayer, melting the mixed powder to form a flux layer that floats on the surface of the melt, controlling reaction temperature, and maintaining the temperature for a certain period; S5, upon stripping off reaction salt residues on the surface, performing mechanical agitation on the melt; S6, sequentially adding alloys of Si, Cu, Cr, Mn, Ti, Zn and Mg, and maintaining the temperature for a certain period to completely melt the elements of the alloys; S7, evenly scattering a slag-cleaning agent onto the surface of the melt by a powder sprayer, introducing high-purity argon with a flow rate of 3 L/h, performing mechanical agitation, stirring and degassing for a certain period, and then stripping off scum on the surface; S8, performing ultrasonic treatment on the melt in the step S7 at an ultrasonic frequency for a certain period; and S9, pouring the melt into a metal mold.
 2. The method for preparation of the aluminum matrix composite according to claim 1, wherein in the step S2, the mixed powder is dried at 200-250° C. for 2-3 h.
 3. The method for preparation of the aluminum matrix composite according to claim 1, wherein in the step S1, an atomic ratio of Ti to B in the K₂TiF₆ powder and the KBF₄ powder is preferably 1:2, and an addition amount of the reaction auxiliary Na₃AlF₆ powder is 10-20% of the total mass of the reaction salt K₂TiF₆ and the reaction salt KBF₄.
 4. The method for preparation of the aluminum matrix composite according to claim 1, wherein in the step S4, the reaction temperature is maintained in the range of 830-850° C. for 30-60 min.
 5. The method for preparation of the aluminum matrix composite according to claim 1, wherein in the step S5, the speed of the mechanical agitation is 250-350 r/min, and the time for the mechanical agitation is 3-5 min
 6. The method for preparation of the aluminum matrix composite according to claim 1, wherein in the step S6, the elements Si, Cr and Mn are respectively added in the form of intermediate alloys AlSi20, AlCr10, AlMn10 and AlTi20, the elements Cu, Zn and Mg are added in the form of pure metals, and the temperature is maintained in the range of 730-750° C.
 7. The method for preparation of the aluminum matrix composite according to claim 1, wherein in the step S7, the speed of the mechanical agitation is 250-350 r/min.
 8. The method for preparation of the aluminum matrix composite according to claim 1, wherein in the step S9, the pouring temperature is in the range of 705-710° C.
 9. The method for preparation of the aluminum matrix composite according to claim 1, wherein in the step S7, stirring and degassing for 5 min, and in the step S8, performing ultrasonic treatment on the melt in the step S7 at an ultrasonic frequency of 20.1 KHz for 10 min. 